1. Field of the Invention
The present invention relates to a motor-driven device for use in a motor-driven coolant pump device in a vehicle engine cooling system, and a motor-driven hydraulic pump device in a vehicle anti-lock braking system or the like.
2. Related Art
In a motor-driven coolant pump device used in a vehicle, as shown in FIG. 5 for instance, a motor 51 is fixed to a pump 50 in a manner exposed externally from the pump 50. Specifically, the motor 51 is fixed to a fixation surface 52a formed on a housing 52 of the pump 50. Its output shaft 53 passes the housing 52 from the fixation surface 52a and protrudes into a pump chamber 54. An impeller 55 is fixed to the output shaft 53 in the pump chamber 54.
A casing 57 of the motor 51 has a bottomed cylindrical yoke 58 and an end plate 59 which closes an opening 58a of the yoke 58. A bearing 60 which supports the output shaft 53 and a brush holder 61 are fitted in the end plate 59.
An O-ring 63 is accommodated in a ring-shaped groove 62 formed on the end plate 59 of the motor 51 and press-fit to the fixation surface 52a so that external splash water may not enter the inside of the motor 51 and the pump chamber 54. Further, an O-ring 66 is held in a stepped part 65 formed in an spigot-joint of the end plate 59 and abuts the inside surface of the yoke 58 so that the external splash water may not enter the inside of the motor 51. Thus, the coolant pump device is constructed to be water-proof.
The end plate 59 is formed by die-cutting a metal plate in the similar manner as the yoke 58 is. Therefore, its dimensional accuracy is not high enough. However, the end plate 59 is required to have a high dimensional accuracy, because the groove 63 or the stepped part 65 requires a high dimensional accuracy for the O-rings 63 and 66 to provide a high sealing performance.
In another motor 69 which requires no O-rings for restricting the splash water from entering, a seal member 68 is fixed to the outer surface of an end plate 67 as shown in FIG. 6. The seal member 68 is constructed from a stack of steel plates each of which is covered with a synthetic resin film 68a. The seal member 68 is pressed to the fixation surface 52a to restrict the splash water from entering the pump chamber 54. Further, a liquid sealant is pasted at the joined surfaces between en end plate 67 and the yoke 58 at the time of assembling to restrict the splash water from entering the inside of the motor 69. The end plate 59 is not required to have a high dimensional accuracy in the motor 69.
However, the accuracy of fixing the motor 69 to the housing 52 in a direction of the output shaft 53 is lessened depending on variations of the synthetic resin film 68a covering the seal member 68, because the motor 69 is fixed to the housing 52 via the seal member 68. The accuracy of assembling the motor 69 in the direction of the output shaft 54 also is lessened, because the liquid sealant is pasted between the end plate 67 and the flange of the yoke 58 to seal the inside of the a casing 70.